Fusion down-draw is a leading technology developed by Corning Incorporated, Corning, N.Y., U.S.A. for making thin, precision glass sheets suitable for use as liquid crystal display (LCD) glass substrates and in other opto-electronic devices. In this process, a stream of molten glass is introduced into a forming trough called isopipe having two side surfaces converging at a line called root via an inlet pipe coupled to the trough of the isopipe. The glass melt is allowed to flow over both top surfaces of the trough side walls of the isopipe called weirs, down along both side surfaces of the isopipe as two molten glass ribbons, and then join and fuse at the root to form a single glass ribbon, which is then drawn down and cooled below the root to form the glass sheet with desired dimension. In the zone below the root, the glass ribbon travels substantially vertically downward while being drawn and cooled from a viscous state, to visco-elastic and eventually to substantially elastic. The elastic glass ribbon is then cut into individual glass sheets, subjected to further finishing such as edge rounding and polishing, and then packaged and shipped to LCD panel makers for use as TFT or color filter substrates. Cutting of the glass ribbon at below the isopipe typically involves the scoring of the ribbon surface, followed by bending along the score-line, whereby discrete glass sheets are separated from the ribbon and then transferred to subsequent steps.
One of the advantages of the fusion down-draw process for making glass sheets is that the surface quality of the glass sheets is high because the quality areas thereof were formed in an atmosphere and never touched a solid material such as the forming equipment. This process has been used successfully for making glass sheets having a width as large as 3000 mm and a thickness of about 0.6 mm.
During cutting and separation of the glass sheet at the bottom of the draw, and during the glass finishing steps such as bead removal, edge chamfering and polishing, a number of glass particles are generated. The glass particles can scratch the glass surfaces, or adhere to the glass surface, which may or may not be removed in a later washing and cleaning step. Any glass particles remaining on the glass surface can cause scratches during the packaging and transportation of the sheet if sheet stacking is required. In addition, during sheet packaging and transportation, additional particles may come into contact with the glass surface, which may reduce the surface quality if insufficient protection is available.
Historical means for protecting LCD glass surfaces include the use of paper, plastic films, coatings such as polysaccharides, surfactants, and the like. However, they suffer from various drawbacks.
Therefore, there remains a need of a method for protecting the surface of glass sheets for which a pristine surface is required during finishing, packaging and transportation. The present invention satisfies this and other needs.